1. The Study of Chemical Reactions
Organic Chemistry, 7th Edition L. G. Wade, Jr.
Chapter 4
The Study of Chemical Reactions
Copyright © 2010 Pearson Education, Inc.

2. Introduction Overall reaction: reactants  products
Mechanism: Step-by-step pathway.
To learn more about a reaction:
Thermodynamics
Kinetics
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3. Chlorination of Methane
Requires heat or light for initiation.
The most effective wavelength is blue, which is absorbed by chlorine gas.
Many molecules of product are formed from absorption of only one photon of light (chain reaction).
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4. The Free-Radical Chain Reaction
Initiation generates a radical intermediate.
Propagation: The intermediate reacts with a stable molecule to produce another reactive intermediate (and a product molecule).
Termination: Side reactions that destroy the reactive intermediate.
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5. Initiation Step: Formation of Chlorine Atom
A chlorine molecule splits homolytically into chlorine atoms (free radicals).
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6. Propagation Step: Carbon Radical
The chlorine atom collides with a methane molecule and abstracts (removes) an H, forming another free radical and one of the products (HCl).
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7. Propagation Step: Product Formation
The methyl free radical collides with another chlorine molecule, producing the organic product (methyl chloride) and regenerating the chlorine radical.
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8. Overall Reaction
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9. Termination Steps
A reaction is classified as a termination step when any two free radicals join together producing a nonradical compound.
Combination of free radical with contaminant or collision with wall are also termination steps.
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10. More Termination Steps
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11. Lewis Structures of Free Radicals
Free radicals are unpaired electrons.
Halogens have 7 valence electrons so one of them will be unpaired (radical). We refer to the halides as atoms not radicals.
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12. Homolytic and Heterolytic Cleavages
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13. Primary, Secondary, and Tertiary Hydrogens
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14. Chlorination Mechanism
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15. Bond Dissociation Energies for the Formation of Free Radicals
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16. Stability of Free Radicals
Free radicals are more stable if they are highly substituted.
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17. Carbon Reactive Intermediates
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18. Carbocation Structure
Carbon has 6 electrons, positively charged.
Carbon is sp2 hybridized with vacant p orbital.
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19. Carbocation Stability
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20. Stability of Carbon Radicals
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21. Carbenes Carbon is neutral. Vacant p orbital, so can be electrophilic.
Lone pair of electrons, so can be nucleophilic.
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